1. Field of the Invention
The present invention relates to an insert rotary cutting tool having plural groups of indexable cutting inserts mounted on an outer periphery of a tool body in circumferentially spaced relation to each other with the inserts of each group being displaced circumferentially of the body and spaced axially of the body.
2. Prior Art
One conventional rotary cutting tool includes an end mill as shown in FIGS. 1 to 3. The end mill comprises a generally cylindrical tool body 100 adapted to be rotated in the direction of the arrow R about an axis O therethrough. The body 100 has a plurality of axially extending slots 102 formed in an outer periphery at its forward end 104 in circumferentially spaced relation to one another, the slots 102 opening to a forward end face of the body 100. Each of the slots 102 has a circumferentially facing wall surface 106 sloping in the circumferential direction opposite to that of rotation of the body 100 away from the forward end face. Formed in each wall surface 106 are a plurality of recesses 108 each opening to the outer periphery of the body 100, those foremost recesses disposed closest to the forward end face of the body 100 also opening to the forward end face. The recesses 108 formed in each slot 102 have respective bottom faces disposed on a plane generally parallel to a respective one of the wall surfaces 106. An indexable cutter insert 110 is received in each recess 108 and fixed in place by a clamp screw 112.
Each insert 110 comprises a quadrilateral plate made of hard wear resistant material such as cemented carbide. Each insert 110 has four main cutting edges formed on four marginal ridges of its front face, and is disposed in such a manner that one of the main cutting edges thereof is indexed in its peripheral cutting position to serve as a peripheral cutting edge 114, and that one of the other main cutting edges of that insert received in each foremost recess is indexed in its end cutting position to serve as an end cutting edge 116. The inserts are also disposed in overlapping relation when the body 100 is viewed in the circumferential direction, so that the peripheral cutting edges 114 of the inserts 110 are disposed continuously in the axial direction.
With this construction, plural groups of the inserts 110 are disposed in the slots 102, respectively, and the peripheral cutting edges 114 of the inserts 110 of each group are disposed on a respective one of a plurality of lines H extending axially helically of the body 100 with equal helix angles .theta. so as to slope in the circumferential direction opposite to that of rotation of the body 100 away from the forward end face. As a result, the respective inserts of each group engage a workpiece one by one and disengage therefrom one by one as the body 100 rotates. Accordingly, cutting loads exerted on the body 100 do not vary abruptly, and therefore the body 100 is prevented from severe vibration during cutting operation.
The prior art end mill, however, has the drawback that it has still been susceptible to a small vibration during cutting operation. Hence, the peripheral cutting edges 114 of the inserts 110 have been susceptible to chipping, and besides the finished surface of the workpiece cut by the end cutting edges 116 has been adversely affected by the vibration. Accordingly, the end mill has not been successfully employed when required to obtain extremely smooth surface finish or when carrying out heavy-duty cutting operation such as deep cutting and high feed cutting.